1. Field of the Invention
This invention relates to storage media and more particularly relates to scaling a tape storage medium to improve data access performance in a tape storage system.
2. Description of the Related Art
Every new generation of tape storage technology is increasing the capacity of tape storage products that are available. The total storage capacity of a tape depends on many factors, including the physical dimensions of the tape, the data compression, if any, used to write data to the tape, the number of tracks across the width of the tape, and so forth. Another factor that may distinguish physical capacity from usable capacity is that the usable capacity is often defined to be slightly less than the physical capacity. This is due, in part, to servo tracks, data block headers, and other metadata blocks throughout the tape.
As total tape storage capacity increases, however, so too does the time required to access data on a tape. For many data storage uses, such as a data backup, longer access time to the data is acceptable. However, many other data storage applications would benefit from faster data access times even though tapes of greater capacity are used in the storage system.
For tape storage applications, data is typically stored onto a magnetic tape medium, such as a metallic ribbon, within a tape cartridge using a tape drive. The tape medium conventionally is designed to include a plurality of tracks that are distributed across the physical width of the tape medium and run the physical length of the tape medium. A tape write head within the tape drive is typically capable of writing up to sixteen tracks at one time, starting at one end of the tape and moving along the length of the tape. When the tape write head reaches the end of the tape, the head is aligned over the proximate track set, the direction of the tape is reversed, and the write head writes an additional sixteen tracks in the opposite direction. This “serpentine” pattern may continue until all tracks have been written.
The process for reading data from the tape medium is essentially the same. A tape read head moves across the tape medium and reads sixteen tracks from one end of the tape medium to the other. The tape read head then realigns to read an additional sixteen tracks and moves over the second set of tracks in the opposite direction.
Given the large capacity of conventional tape storage devices, various data blocks may be stored on a single tape medium. The location of each of these data blocks may be marked on the tape using block header information, data pads (areas of tape where data is intentionally not written), and other conventional identification means and methods. The tape read head is able to locate a particular block of data by using one or more servo tracks that are written onto the tape storage medium.
More recently, manufacturers of tape storage products have directed their attention in part to improving data access time using tape storage drives and cartridges. One method that has been employed to address the problem of increased data access time is to employ various levels of transparent buffering in which tape data may be stored on other storage medium, such as a direct access storage device (DASD) or an optical disk. If the requested tape data is stored on a DASD cache, data retrieval time may be improved greatly. However, the storage capacity of a DASD cache is typically significantly less than that of a con tape storage system. Similarly, the storage capacity of an optical disk is much less than that of a tape cartridge. Currently, technology allows as much as 300 Gb of non-compacted data to be stored on a single, standard tape cartridge compared to approximately 5 Gb of data on an optical disk.
Another method of improving data access time is to segment the tape storage medium into two or more segments and to write data to the segments in a sequential manner. A tape segment may include a specified capacity, or physical length of tape, that is less than the total capacity of the tape. For example, a tape storage medium may be divided into two segments. When writing data to the tape, the data is written to the first segment until full and then to the second segment. This method decreases data access time in that the first segment may be written or read without physically forwarding all the way to the end of the tape storage medium.
Finally, tape storage medium may be scaled to increase data access performance. A scaled tape storage medium is somewhat similar to a segmented tape storage medium in that both storage devices have logically limited capacities to decrease the amount of tape that must be traversed while reading data. The difference between segmented and scaled basically is that a scaled device may only be used to the logically limited capacity and a segmented device may be used to the full capacity of the tape storage medium.
Unfortunately, certain applications are not programmed to realize the benefits of scaling a tape storage medium. The hardware and tape controllers are configured to support scaling, but the applications may not be. In addition, it is desirable to have a predefined capacity that balances the tape media storage capacity and data access performance. Such a predefined capacity may be referred to as an optimal performance capacity. These applications would have to be altered to utilize scaling as well as the optimal performance capacity.
Accordingly, what is needed is a process, apparatus, and system for improving data access performance of a tape storage system using tape media scaling. Beneficially, such a process, apparatus, and system would allow a user to take advantage of the tape media scaling in order to quickly access specified data, and without the added burden of altering each application that uses the tape storage media.